电沉积法和混凝沉淀法组合工艺回收处理含镉废水的研究
发布时间：2019-04-23 14:07
【摘要】：镉是一种重金属，可以致癌。如果在环境中通过饮用水或者食物链进入人体将对人类造成很大的危险。所以在工业上或者水源里对镉的去除至关重要。本文用电沉积法和混凝法组合工艺处理高浓度的含镉废水，在回收镉金属的同时，使处理后水体的镉浓度达到《污水综合排放标准》(GB8978-1996)规定的0.1mg/L排放标准。 在电沉积过程中，利用电沉积的方法回收将废水中的镉，，实验中在电解槽内采用多阴阳极反应器内分别考察不同初始浓度的含镉废水（400mg/L、600mg/L、1000mg/L）、不同初始pH（1.5、3.5、5.5、7.5）、不同电流密度（1.49mA/cm2、2.97mA/cm2、4.46mA/cm2、5.95mA/cm2）、不同电解质种类及浓度（NaCl、NaNO3、Na2SO4）、不同腐殖酸浓度和络合物对电沉积含镉废水的影响。实验结果表明在工作电极为钛板的三相电极中，镉的还原电位为-0.64V到-0.78V。一级动力学常数和电流效率随着镉的初始浓度的增加而增加。当电流密度从1.49mA/cm2增到4.46mA/cm2时,在120分钟电沉积时间内，镉的回收率从96.98%上升到99.3%，此时再增加电流密度，镉的回收效率和电流效率都不会再增加。当溶液中存在硝酸钠电解质时，会使镉的反应速率下降。当溶液中存在腐殖酸的浓度为200mg/L时，在前60分钟，镉的反应速率很慢，但是随着腐殖酸被氧化，在后60分钟，反应速率则加快。氨水的存在会促进电沉积镉的反应速率。通过采用扫描电镜和能谱、X射线衍射仪和X射线光电子能谱仪对沉积物进行分析发现：在电沉积过程中，废水中的主要以单质镉和氢氧化镉的形式被沉淀。 在混凝沉淀阶段，研究不同pH值（5.0、6.0、7.0、8.0、9、0）、不同Al存在形式的絮凝剂和不同投加量对镉去除效果的影响。实验结果表明初始pH为9的溶液，镉的去除效果较好。以Al存在形式的高聚物比低聚物和中聚物去除镉效果很好。当随着聚合氯化铝（PAC）投加量增加，当PAC投加量大于0.4mL，溶液中的镉去除率高达90%，说明只要投加少量的PAC，就可以起到很好的混凝效果。当随着聚合氯化铝（PAC）投加量增加，Al的存在形式以高聚物为主，镉的去除效果明显增加。对絮体进行XRD表征发现絮体主要以碳酸镉和氢氧化镉的形式存在。
[Abstract]:Cadmium is a heavy metal that can cause cancer. If you enter the human body through drinking water or food chain in the environment, it will be a great danger to human beings. Therefore, the removal of cadmium in industry or in water sources is essential. In this paper, the combined process of electrodeposition and coagulation is used to treat the wastewater containing high concentration of cadmium. While recovering cadmium metal, the concentration of cadmium in the treated water reaches the 0.1mg/L discharge standard stipulated in the Integrated Wastewater discharge Standard (GB8978-1996). In the process of electrodeposition, cadmium in the wastewater was recovered by electrodeposition. In the experiment, the cadmium-containing wastewater with different initial concentrations (400 mg / L, 600 mg / L, 1000 mg / L) was investigated in a multi-cathode and anode reactor in an electrolytic cell. Different initial pH (1.5, 3.5, 5.5, 7.5), different current densities (1.49 Ma / cm 2, 2.97 Ma / cm 2, 4.46 Ma / cm 2, 5.95 Ma / cm 2), different electrolyte types and concentrations (NaCl,NaNO3,Na2SO4), Effect of humic acid concentration and complex on electrodeposition of cadmium-containing wastewater. The experimental results show that the reduction potential of cadmium is-0.64 V to-0.78 V. in the three-phase electrode with titanium plate as the working electrode. The first order kinetic constant and current efficiency increase with the increase of initial concentration of cadmium. When the current density increases from 1.49mA/cm2 to 4.46mA/cm2, the recovery rate of cadmium increases from 96.98% to 99.3% in 120min electrodeposition time. When the current density is increased, the recovery efficiency and current efficiency of cadmium will not increase any more. When sodium nitrate electrolyte exists in the solution, the reaction rate of cadmium will decrease. When the concentration of humic acid in the solution is 200mg/L, the reaction rate of cadmium is very slow in the first 60 minutes, but increases with the oxidation of humic acid in the last 60 minutes. The presence of ammonia can promote the rate of electrodeposition of cadmium. By means of scanning electron microscopy and energy spectrum, X-ray diffractometer and X-ray photoelectron spectroscopy, it is found that in the process of electrodeposition, the waste water is mainly precipitated in the form of cadmium hydroxide and cadmium hydroxide. The effects of different pH values (5.0, 6.0, 7.0, 8.0, 9, 0), different forms of flocculants in the presence of Al and different dosages on the removal of cadmium were studied in the coagulation and sedimentation stage. The effects of different pH values (5.0, 6.0, 7.0, 8.0, 9, 0) on the removal of cadmium were studied. The experimental results show that the removal effect of cadmium is better when the initial pH is 9. The removal of cadmium by polymer in the form of Al is better than that of oligomer and polymer. When the dosage of polyaluminum chloride (PAC) increases, when the dosage of PAC is more than 0.4 mL, the removal rate of cadmium in the solution is as high as 90%, indicating that the coagulation effect can be achieved by adding a small amount of PAC,. With the increase of the dosage of polyaluminum chloride (PAC), the existence of Al was mainly in the form of polymer, and the removal efficiency of cadmium was obviously increased. The floc was characterized by XRD. It was found that the floc was mainly in the form of cadmium carbonate and cadmium hydroxide.
【学位授予单位】：南华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：X703.1;TQ150
[Abstract]:Cadmium is a heavy metal that can cause cancer. If you enter the human body through drinking water or food chain in the environment, it will be a great danger to human beings. Therefore, the removal of cadmium in industry or in water sources is essential. In this paper, the combined process of electrodeposition and coagulation is used to treat the wastewater containing high concentration of cadmium. While recovering cadmium metal, the concentration of cadmium in the treated water reaches the 0.1mg/L discharge standard stipulated in the Integrated Wastewater discharge Standard (GB8978-1996). In the process of electrodeposition, cadmium in the wastewater was recovered by electrodeposition. In the experiment, the cadmium-containing wastewater with different initial concentrations (400 mg / L, 600 mg / L, 1000 mg / L) was investigated in a multi-cathode and anode reactor in an electrolytic cell. Different initial pH (1.5, 3.5, 5.5, 7.5), different current densities (1.49 Ma / cm 2, 2.97 Ma / cm 2, 4.46 Ma / cm 2, 5.95 Ma / cm 2), different electrolyte types and concentrations (NaCl,NaNO3,Na2SO4), Effect of humic acid concentration and complex on electrodeposition of cadmium-containing wastewater. The experimental results show that the reduction potential of cadmium is-0.64 V to-0.78 V. in the three-phase electrode with titanium plate as the working electrode. The first order kinetic constant and current efficiency increase with the increase of initial concentration of cadmium. When the current density increases from 1.49mA/cm2 to 4.46mA/cm2, the recovery rate of cadmium increases from 96.98% to 99.3% in 120min electrodeposition time. When the current density is increased, the recovery efficiency and current efficiency of cadmium will not increase any more. When sodium nitrate electrolyte exists in the solution, the reaction rate of cadmium will decrease. When the concentration of humic acid in the solution is 200mg/L, the reaction rate of cadmium is very slow in the first 60 minutes, but increases with the oxidation of humic acid in the last 60 minutes. The presence of ammonia can promote the rate of electrodeposition of cadmium. By means of scanning electron microscopy and energy spectrum, X-ray diffractometer and X-ray photoelectron spectroscopy, it is found that in the process of electrodeposition, the waste water is mainly precipitated in the form of cadmium hydroxide and cadmium hydroxide. The effects of different pH values (5.0, 6.0, 7.0, 8.0, 9, 0), different forms of flocculants in the presence of Al and different dosages on the removal of cadmium were studied in the coagulation and sedimentation stage. The effects of different pH values (5.0, 6.0, 7.0, 8.0, 9, 0) on the removal of cadmium were studied. The experimental results show that the removal effect of cadmium is better when the initial pH is 9. The removal of cadmium by polymer in the form of Al is better than that of oligomer and polymer. When the dosage of polyaluminum chloride (PAC) increases, when the dosage of PAC is more than 0.4 mL, the removal rate of cadmium in the solution is as high as 90%, indicating that the coagulation effect can be achieved by adding a small amount of PAC,. With the increase of the dosage of polyaluminum chloride (PAC), the existence of Al was mainly in the form of polymer, and the removal efficiency of cadmium was obviously increased. The floc was characterized by XRD. It was found that the floc was mainly in the form of cadmium carbonate and cadmium hydroxide.
【学位授予单位】：南华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：X703.1;TQ150
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